The present invention relates to a new and improved method and control apparatus for separating the rolls of a roll calender, in other words to open the roll calender.
Generally speaking, the roll calender or simply calender comprises a stand and a plurality of superimposed rolls are supported by the stand. The bottom or lowermost roll of this stack or set of superimposed rolls comprises a non-rotatably mounted carrier or support beam which is substantially vertically movable by means of fluid-operated, typically hydraulic support devices. This bottom roll further contains a roll shell rotatable about the non-rotatable carrier or support beam. The roll shell is supported by at least one hydraulic support or pressure element against the non-rotatable carrier or support beam and is movable in substantially vertical direction. The pressure which is effective both in the hydraulic carrier support devices and at the hydraulic roll shell support elements, is reduced, so that both the non-rotatable carrier or support beam and the roll shell are moved substantially vertically downwards in order to open the calender.
Such a method is known to the art through placement of such a calender into operation in the Augsburg factory of Haindl Papier GmbH, of West Germany, on Jan. 17, 1980.
This roll calender or calender essentially corresponds to the construction described in U.S. Pat. No. 3,884,141, wherein the bottom or lowermost roll is constructed as a so-called sag compensation roll or controlled deflection roll of the type described in U.S. Pat. No. 3,885,283, granted May 27, 1975, in which the roll shell is freely movable with respect to the carrier or support beam in vertical direction within the degree of the freedom of movement or motion clearance of the support or pressure elements. The carrier or support beam is additionally supported at its ends or bearings with respect to the roll stand by means of hydraulic, e.g. hydrostatic support devices. The closing of the calender, i.e. the raising of the complete stack or set of rolls takes place by pressurizing or pressure impingement of both the hydraulic roll shell support elements and the hydrostatic carrier support devices.
It is also possible to rapidly open the calender, i.e. rapidly lower the complete roll stack or set until the individual rolls rest on associated stops, in that both the pressure acting upon the hydraulic roll shell support elements and upon the hydrostatic carrier support devices is reduced by opening corresponding valves. Through the movement of both the non-rotatable carrier or support beam with respect to the roll stand and the roll shell with respect to the non-rotatable carrier, particularly in the case of calenders for the processing of paper, plastic or other materials, when a fault occurs, e.g. tearing of a web, it is possible to rapidly separate the calender rolls from one another and therefore the risk of damage is reduced to the minimum.
In the similarly constructed calender described in German Pat. No. 3,004,912, it is proposed to simultaneously open the valves of the pressure lines or conduits for the carrier support devices and the roll shell support elements. When using this method or technique with simultaneously commencing lowering of the carrier and roll shell, difficulties were however encountered, particularly in the case of calenders operating with a high pressing pressure or force and when attempting to obtain particularly short roll separating times, in other words, during rapid opening of the roll calender. On the one hand, it was not readily possible to reduce the separating time of the roll stack to the desired short times and, on the other hand, particularly in the case of high pressing pressures, there occurred damage, such as fissures or fractures of the roll shell of the controlled deflection roll, the cause of which was apparently not readily discernible or understood.